Expert: Don’t Let Up on Fighting Water Weed: Thanks to Grass Carp, No Sign of Hydrilla Since ’05

By Erica Beshears, The Charlotte Observer, N.C.

Apr. 12–A national expert on aquatic weed management recommends that Lake Norman leaders continue to aggressively fight hydrilla with grass carp for years, even though the problem appears under control.

Duke Energy crews have not spotted hydrilla in the lake since 2005, proof that the grass carp — a hungry vegetarian fish — are doing their job.

But hydrilla tubers in the soil can lay dormant up to 10 years before sending up new shoots. And the reintroduction of hydrilla or other invasive water plants is likely, based on the way the weeds have spread in lakes in the Southeast, said Phil Kirk, a fisheries biologist for the U.S. Army Corps of Engineers.

“I think it’s something you’ve got to count upon,” Kirk said. “It’s really important that you never allow hydrilla to get established here. No good will come of getting it established.”

Hydrilla is a non-native water weed that grows aggressively in water up to 20 feet deep. At first, it appears to provide fish and wildlife habitat. But as it grows unchecked, hydrilla can clog intakes for drinking water and energy production, choke boat propellers and make swimming dangerous.

The situation never got that dire in Lake Norman, where in 2004, hydrilla had infested about 400 acres. The Lake Norman Marine Commission hired Kirk as a consultant, and he recommended that sterile grass carp be used to eat the plant. The non-native carp, sterile so they can’t reproduce, cost less than chemical herbicides and Kirk believes they’re more effective.

The fish did their job more quickly than expected, and local leaders believe that early intervention saved money. Bob Elliott, assistant executive director for the Lake Norman Marine Commission, pointed out that the government will spend $1 million this year to fight hydrilla in Lake Gaston to the northeast, compared with $1,000 for a supplemental stocking of grass carp in Lake Norman.

This year, Kirk will update the management plan for the next 15 years. A key component of the update will be sampling the grass carp population to determine how long the fish are living.

The sampling, tentatively planned for a weekend in September, will involve recruiting skilled bow-fishers to hunt the grass carp. Then Kirk, along with scientists with Duke Energy and the state, will determine the fish’s length and weight. Kirk can determine the carp’s age by removing and studying a small bone, similar to counting rings in a tree.

The fish mortality rate will help Kirk decide how many carp should be stocked in Lake Norman each year to keep a minimum number of fish in the water to eat any new hydrilla shoots that start to grow, and nip a new infestation of any exotic plant in the bud.

Duke Energy scientist Ken Manuel, a member of the N.C. Aquatic Weed Control Council, also said a new infestation of hydrilla or other invasive plants is likely.

Hydrilla can be easily spread from lake to lake by boats that get the weed caught in their propellers. Ducks and geese can spread it, he said. Also, some fishermen who believe the lake needs more vegetation could introduce it. Manuel also worries about lake dwellers’ backyard water gardens.

Residents should never empty the contents of a water garden into the lake because they might not know what exotic species they’re introducing. “There’s many other submerged aquatic species that can cause problems,” he said.

Hydrilla on Other Lakes

Lake Norman isn’t the only local lake to have problems with hydrilla. Mountain Island Lake and Lake James have both fought infestations in recent years, and hydrilla was recently discovered on Lake Wylie.

Lake Hickory and Lookout Shoals, the small lake north of Lake Norman, have had problems with another weed, called parrotfeather.

—— Erica Beshears: 704-987-3670, ext. 11

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Copyright (c) 2007, The Charlotte Observer, N.C.

Distributed by McClatchy-Tribune Business News.

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